Pumps are used in a variety of applications and fields to move fluid from one location to another. A gear shaft assembly of one type of such a pump 10 is shown in FIG. 1. As illustrated in that figure, the pump 10 includes a housing 12 defining two oppositely disposed bores 14, 16 and a cavity 18. A threaded retainer 20 is threaded into one of the bores 14. The retainer 20 is annular. One end of a shaft 22 is fixedly secured within the opening defined by the annular retainer 20. The other end of the shaft 22 is fixedly secured in the bore 16. Typically, the retainer 20 is secured in the bore 14 with an adhesive such as retainer #680 which is commercially available from LocTite.TM.. The ends of the shaft 22 are also secured in the retainer 20 and the bore 16 using a similar adhesive.
A gear assembly 26 is mounted on the shaft 22 for free rotation thereabout. The gear assembly 26 is located on the shaft by a spacer 27. The gear assembly 26 typically includes a toothed gear 28 and an eccentric (not shown in FIG. 1). The toothed gear 28 is usually driven to rotate by a motor or the like coupled to the gear 28 by a drive train which may include a worm gear (not shown). The rotation of the gear 28 about the shaft 22 causes the eccentric to rotate. The eccentric is commonly coupled to a piston (not shown) via a crank 30. The rotation of the eccentric, thus, causes the piston to reciprocate. The reciprocation of the piston is used to create a pumping force which, with suitably arranged conventional valving, is used to move fluid through a conduit or the like.
While pumps employing gear shaft assemblies of the foregoing type are very effective, they do suffer from certain disadvantages. For example, such gear shaft assemblies include a relatively large number of parts, are complicated to build and require extensive assembly time. Because they are assembled with adhesive, such assemblies are also difficult to disassemble and, thus, similarly difficult to repair. Specifically, it is typically necessary to heat the adhesive to disassemble the unit. The gear shaft assemblies of the foregoing type are also disadvantaged in that they are susceptible to leakage through the opposed bores 14, 16. Moreover, the primer and adhesive used to clean and adhere the parts of the assembly together cause skin irritations to the assemblers and may include harmful chemicals. The confined area within the housing, and the difficulty of properly locating the threaded bushing 20 in the housing also increase the effort required to assemble the gear shaft assemblies of the foregoing type.
Some of the above noted disadvantages are evident in the assembly process required to construct the gear shaft assembly of FIG. 1. Specifically, to construct the subject assembly, one must first clean the housing 12 at the threaded bushing bore 14 and the bore 16 with a cleaning solvent such as Primer #7649 sold by LocTite.TM.. Then, a mechanical stop (not shown) must be installed within the housing 12 to aid in properly locating the threaded bushing 20 within the bore 14. The threaded bushing 20 is next cleaned with the noted solvent, and a liberal quantity of the above-noted adhesive is applied to the threads of the bushing 20 and/or the bore 14. The bushing 20 is then screwed into the bore 14 until it abuts the mechanical stop. The assembly is next allowed to sit for a few minutes while the adhesive cures.
The spacer 27 is then positioned within the housing 12 and the shaft 22 is inserted through the bore 16 and the spacer 27. The shaft 22 is advanced until it is flush with the inner side of the spacer 27. The pre-assembled eccentric/gear assembly 26 is then loaded into the housing 12 and positioned with its shaft hole in alignment with the shaft 22. The end of the shaft 22 extending outside the housing 12 is then tapped to drive the shaft through the gear assembly such that the shaft 22 stops just short of the hole defined in the threaded bushing 20.
Adhesive is then applied to the portion of the shaft 22 still remaining outside the housing 12 and to the inside surface defining the hole of the threaded bushing 20. The shaft 22 is then taped into place such that its ends are flush with both sides of the housing 12. Any excess adhesive is then wiped off the sides of the housing 12.